As in, can you list them all without checking an online walkthrough or anything; I can do this with Lemmings but not with ONML.
Or, I can do it with most of Lemmings. For some reason I forget the names of some fun levels.

Do I know the solution to every level in both original and Oh No? Yes! Do I know the name and order of every level? No! Who would want to? O_o

I don't know, but I've played Lemmings so much I can list most levels in order. Roughly.

Say if I gave you the name of a level, would you be able to picture it and its solution?

With most levels.

I used to have the titles of every level of Super Mario World 2 memorized. I kind of forgot a few now.

For Lemmings, I can, given a title, picture the level and its solution, although given merely a category/number (E.G., Taxing 22), I can't do that for EVERY level.

I remember a fair amount of them for the original Lemmings and Lemmings Revolution. I don't remember them in order, though, and am liable to forget in a pinch.
I remember some of the others as well, of course, just not as many.

In short, no, I'm afraid I can't do that. I kinda wish I could, though...